Supramolecular Architectures and Magnetic Properties of Coordination Polymers Based on Pyrazinedicarboxylato Ligands Showing Embedded Water Clusters Garikoitz Beobide, Oscar Castillo,* Antonio Luque, Urko Garcı ´a-Couceiro, Juan P. Garcı ´a-Tera ´n, and Pascual Roma ´n Departamento de Quı ´mica Inorga ´ nica, Facultad de Ciencia y Tecnologı ´a, UniVersidad del Paı ´s Vasco/Euskal Herriko Unibertsitatea, Apartado 644, E-48080 Bilbao, Spain Received February 8, 2006 The synthesis, crystal structure, and magnetic behavior of nine transition-metal complexes based on pyrazine-2,5- dicarboxylato (pz25dc) and pyrazine-2,3-dicarboxylato (pz23dc) ligands are reported. The pz25dc ligand displays a bis-bidentate coordination mode, with the carboxylate groups almost coplanar with the pyrazine ring, to afford polymeric 1-D chains [Mn(1), Fe(2), Zn(3), and Cu(4 and 5)] and discrete dimeric entities [Mn(6)] when the 1,10- phenanthroline (phen) blocking ligand is used to avoid further polymerization. The nonplanar pz23dc ligand chelates to a unique copper center, while it bridges another one or two metal centers via the remaining carboxylate group, leading to 1-D polymeric chains (7), ladder chains (8), and sheets (9). The crystal packing of the metal-organic frameworks of compounds 4-9 generates voids which are occupied by assembled water molecules. The different water cluster patterns (tapes, four-membered discrete rings, and chains for compounds 6, 8, and 9, respectively) and their role in the cohesiveness of supramolecular architectures are analyzed. Thermogravimetric and variable- temperature X-ray powder diffraction studies have revealed the occurrence of reversible dehydration processes in compounds 6, 8, and 9. Furthermore, the magnetic behavior of these compounds has been studied in order to analyze the capability of the pyrazine ring to transmit magnetic interactions. Introduction In recent years, the area of inorganic crystal engineering 1 has become one of intense research activity because of the growing need for novel solid-state architectures with potential applications as functional materials in fields such as catalysis, conductivity, zeolitic behavior, and magnetism. 2 The judi- cious choice of the metal ion, a good understanding of the coordination preferences of the bridging entities, and a careful selection of the terminal ligands are key steps for the rational design of metal-organic coordination polymers with novel topologies and specific chemical and physical properties. 3 In this context, π-conjugated N-donor bridging ligands, such as pyrazine and its polycarboxylic derivatives, have appeared to be well-suited tools for the construction of extended arrays of metal ions with interesting physical properties in molecular magnetism or selective guest adsorption fields. 4,5 Among them, the synthesis and characterization of metal coordination polymers based on the pyrazine-2,3-dicarboxylato (pz23dc) ligand has evolved rather rapidly in recent years, 5,6 mostly because of two reasons: (a) the presence of two carboxylate * To whom correspondence should be addressed. Phone: 34 946-015- 991. Fax: 34 944-013-500. E-mail: oscar.castillo@ehu.es. (1) (a) Brammer, L. Chem. Soc. ReV. 2004, 33, 476-489. (b) Braga, D.; Brammer, L.; Champness, N. R. CrystEngComm. 2005, 7,1-19. (2) (a) James, S. L. Chem. Soc. ReV. 2003, 32, 276-288. (b) Janiak, C. J. Chem. Soc., Dalton Trans. 2003, 2781-2804. (3) (a) Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40, 2022-2043. (b) Braga, D.; Desiraju, G. R.; Miller, J. S.; Orpen, A. G.; Price, S. L. CrystEngComm. 2002, 4, 500-509. (4) (a) O’Connor, C. J.; Klein, C. L.; Majeste, R. J.; Trefonas, L. M. Inorg. Chem. 1982, 21, 64-67. (5) (a) Kondo, M.; Okubo, T.; Asami, A.; Noro, S. I.; Yoshitomi, T.; Kitagawa, S.; Ishii, T.; Matsuzaka, H.; Seki, K. Angew. Chem., Int. Ed. 1999, 38, 140-143. (b) Kitaura, R.; Fujimoto, K.; Noro, S.; Kondo, M.; Kitagawa, S. Angew. Chem., Int. Ed. 2002, 41, 133-135. (c) Li, D.; Kaneko, K. J. Phys. Chem. B 2000, 104, 8940-8945. (d) Maji, T. K.; Uemura, K.; Chang, H.-C.; Matsuda, R.; Kitagawa, S. Angew. Chem., Int. Ed. 2004, 43, 3269-3272. (6) (a) Gryz, M.; Starosta, W.; Ptasiewciz-Bak, H.; Leciejewicz, J. J. Coord. Chem. 2003, 56, 1575-1579. (b) Konar, S.; Manna, S. C.; Zangrando, E.; Chaudhuri, N. R. Inorg. Chim. Acta 2004, 357, 1593- 1597. (c) Premkumar, T.; Govindarajan, S. Inorg. Chem. Commun. 2003, 6, 1385-1389. (d) Zou, J.-Z.; Xu, Z.; Chen, W.; Lo, K. M.; You, X.-Z. Polyhedron 1999, 18, 1507-1512. (e) Liang, Y.; Hong, M.; Cao, R.; Su, W.; Zhao, Y.; Weng, J.; Xiong, R. Bull. Chem. Soc. Jpn. 2002, 75, 1521-1526. Inorg. Chem. 2006, 45, 5367-5382 10.1021/ic060221r CCC: $33.50 © 2006 American Chemical Society Inorganic Chemistry, Vol. 45, No. 14, 2006 5367 Published on Web 06/07/2006